[PATCH v15 4/9] namei: LOOKUP_BENEATH: O_BENEATH-like scoped resolution

[Aleksa Sarai]

On 2019-11-13, Al Viro <viro at zeniv.linux.org.uk> wrote:
> Minor nit here - I'd split "move the conditional call of set_root()
> into nd_jump_root()" into a separate patch before that one.  Makes
> for fewer distractions in this one.  I'd probably fold "and be
> ready for errors other than -ECHILD" into the same preliminary
> patch.

Will do.

> > +			/* Not currently safe for scoped-lookups. */
> > +			if (unlikely(nd->flags & LOOKUP_IS_SCOPED))
> > +				return ERR_PTR(-EXDEV);
> 
> Also a candidate for doing in nd_jump_link()...
> 
> > @@ -1373,8 +1403,11 @@ static int follow_dotdot_rcu(struct nameidata *nd)
> >  	struct inode *inode = nd->inode;
> >  
> >  	while (1) {
> > -		if (path_equal(&nd->path, &nd->root))
> > +		if (path_equal(&nd->path, &nd->root)) {
> > +			if (unlikely(nd->flags & LOOKUP_BENEATH))
> > +				return -EXDEV;
> 
> Umm...  Are you sure it's not -ECHILD?

It wouldn't hurt to be -ECHILD -- though it's not clear to me how likely
a success would be in REF-walk if the parent components didn't already
trigger an unlazy_walk() in RCU-walk.

I guess that also means LOOKUP_NO_XDEV should trigger -ECHILD in
follow_dotdot_rcu()?

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>
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